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Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Mikami, Satoshi; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanaizuka, Seiichi*; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*
Environmental Science & Technology, 194, p.109148_1 - 109148_8, 2024/12
Times Cited Count：0 Percentile：0.00(Environmental Sciences)Assessment of individual external doses from ambient dose equivalents is used for predictive and retrospective assessments where personal dosimeters are not applicable. However, it tends to contain more errors than assessment by personal dosimetry due to various parameters. Therefore, in order to accurately assess the individual dose from ambient dose equivalents, a model that estimates effective doses considering life patterns and the shielding effects by buildings and vehicles, were developed in this study. The model parameters were examined using robust datasets of environmental radiation measured in the areas affected by the Fukushima Daiichi Nuclear Power Station accident in 2020 to 2021. The accuracy of the model was validated by comparison with 106 daily personal doses measured in Fukushima Prefecture in 2020. The measured personal dose was well reproduced by the model-estimated effective dose, showing that the model can be used to assess the individual exposure dose, similar to personal dosimetry. Furthermore, this model is an effective tool for radiation protection, as it can estimate the individual dose predictively and retrospectively by using environmental radiation data.
Sanada, Yukihisa; Abe, Tomohisa; Sasaki, Miyuki; Kanno, Marina*; Yamada, Tsutomu*; Nakasone, Takamasa*; Miyazaki, Nobuyuki*; Oshikiri, Keisuke*; Watabe, Hiroshi*
Journal of Nuclear Science and Technology, 61(5), p.693 - 702, 2024/05
Times Cited Count：5 Percentile：85.83(Nuclear Science & Technology)The "treated water" from which the main radioactive materials were removed contains tritium, and stakeholders in Japan have been debating how to treat it. The amount of treated water stored in the facility has reached its limit, and the Japanese government has decided that the treatment method will be to discharge the water into the ocean by FY 2023 (FY: Fiscal Year). The present research developed a simple and practical tritium monitor for the Fukushima Daiichi Nuclear Power Station (FDNPS) tritiated water release. A simple and practical tritium monitor was developed for FDNPS tritiated water release based on thin plastic scintillator sheets. The developed devices were calibrated using standard tritium solutions and a method for calculating the minimum detectable activity. Fifteen 0.25 mm-thick scintillators can be placed in the 0.26 L flow cell where the sample water is fed, yielding an active surface area of 3,200 mm
. The efficiency of tritiated water with full water is 0.000035 cps Bq
. The minimum detectable activity under simple shielding conditions was 7,800 Bq L (Measurement time was 3,600 s).
Sanada, Yukihisa; Miyamoto, Kenji*; Momma, Hiroyasu*; Miyazaki, Nobuyuki*; Nakasone, Takamasa*; Tahara, Junichiro*; Baba, Shoichiro*; Furuyama, Hiroki*
Marine Technology Society Journal, 55(5), p.222 - 230, 2021/09
Large quantities of volatile radionuclides were released into the atmosphere following the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in March 2011. To evaluate their effect on aquatic organisms and radiocesium behavior in the environment, the monitoring of radioactive cesium in the waterbed soil is important. We developed a dedicated radiation survey device that can both directly measure and collect some sediment samples. A comprehensive test was conducted using this device, which was installed in an unmanned surface vehicle at Fukushima offshore contaminated by radiocesium that resulted from the FDNPS accident. Consequently, the effectiveness of this device was confirmed because the measurement results of the sediment-core sample and in-situ radiation survey results show a good correlation. A successful application of this device in the time of post-nuclear facility accident is expected.
(Ce) detector for estimating radiocesium distribution in soilOchi, Kotaro; Malins, A.; Ishida, Mutsushi*; Yamada, Tsutomu*; Nakasone, Takamasa*; Sanada, Yukihisa
no journal, ,
no abstracts in English
(Ce) detector used for estimating radiocesium distribution in soilMalins, A.; Ochi, Kotaro; Nakasone, Takamasa*; Yamada, Tsutomu*; Machida, Masahiko; Kurikami, Hiroshi; Saito, Kimiaki; Sanada, Yukihisa
no journal, ,
Here we report PHITS Monte Carlo simulations of a LaBr(Ce) gamma spectroscopy system used in unmanned helicopter radiation surveys in Fukushima Prefecture. The simulated spectra were verified against measurements taken under controlled laboratory conditions. Simulations were used to characterize the peak-to-Compton method for estimating the vertical distribution of radiocesium in soil from airborne surveys.
Morishita, Yuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
no journal, ,
The Fukushima Daiichi Nuclear Power Station's decommissioning requires thorough inspection of piping for contamination, including alpha nuclides. External alpha particle measurements are impossible, necessitating gamma-ray detection methods. A phoswich detector for low-energy gamma-ray detection was developed and validated experimentally at a nuclear fuel facility. The detector was designed considering energy deposition characteristics. The detector comprises YAlO:Ce and Bi
GeO
scintillators with a photomultiplier tube for signal amplification. Measurement and simulation results show correlation between scintillator energy depositions for different gamma-ray energies. Pulse Shape Discrimination (PSD) plots distinguish alpha particles and gamma-rays, confirming simulation predictions. Nuclear fuel facility measurements exhibit higher energy deposition in the first scintillator layer. This suggests potential for developing a sensitive low-energy gamma-ray detector using scintillator combinations. Future work aims to optimize detector design and conduct field tests for validation.
Morishita, Yuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
no journal, ,
We have tried to create a novel compact alpha/beta detector capable of direct insertion into piping for the immediate assessment of alpha and beta contamination. The detector, a phoswich detector, comprises scintillators for alpha and beta particles. For alpha particles, a ZnS(Ag) scintillator with a thickness of 3.25 mg/cm was used as the initial layer, while a cerium-doped GdGaAl
O (GGAG) scintillator measuring 6 mm 
6 mm 6 mm served as the scintillator for the secondary layer for beta particles. The bottom of the GAGG scintillator was coupled with optical grease to a compact photomultiplier tube (H14603, Hamamatsu Photonics K.K.), with an effective diameter of 8 mm
. The signal was amplified by a preamplifier embedded in the compact photomultiplier tube and then the signal was input to a digitizer (DT5730S, CAEN). to confirm the alpha/beta discrimination performance. Subsequently, a thorium source emitting alpha and beta particles concurrently conducted measurement. A charge integration (CI) method was employed to distinguish the alpha and beta waveforms. A 2-dimensional Pulse Shape Discrimination (PSD) map showed the distribution of two clusters of alpha and beta particles, both of which were effectively discriminated. The detector has outer dimensions of 22.0 mm 22.0 mm 30.0 mm, facilitating direct insertion into a pipe for measurement purposes. As a future endeavor, we aim to optimize the discrimination between alpha and beta particles by modifying the combination of scintillators.
Sasaki, Miyuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Sanada, Yukihisa
no journal, ,
no abstracts in English
